I. Field of the Invention
The present invention relates to a variable compression ratio (VCR) piston assembly, such as those disclosed in U.S. Pat. Nos. 3,156,162; 3,161,112; 3,185,137; 3,185,138; 3,303,831; 3,311,096; 3,403,662; 3,418,982; 3,450,111; 3,417,738; 3,417,739; 3,450,112; 3,527,264; 3,405,698; 3,405,697; 3,450,113; 3,407,791; 3,667,433; 3,704,695; 4,016,841 and 4,031,868; all owned by applicants' assignee and more particularly to an improved construction for such piston assemblies.
II. Description of the Prior Art
In the constructions disclosed in the patents indicated above an inner piston member is connected in the usual manner to a connecting rod while an outer piston member is carried by and is movable axially relative to the inner member. Relative movement of these members varies the compression ratio of the particular cylinder in which the piston moves. Clearance spaces are provided between the top and bottom ends of the inner and outer members, respectively, and these form upper and lower chambers which vary conversely in volume in relation to the relative movement of the piston members. An essentially incompressible fluid, such as the engine lubrication oil, is supplied to these chambers in a manner which automatically regulates movement of the members to gradually change the compression ratio until a predetermined combustion pressure has been achieved. The hydraulic system then varies the movement of the members in a manner which tends to maintain a uniform maximum combustion chamber pressure.
Conventionally, the hydraulic system for these previously known VCR piston assemblies include both a supply passage and a discharge passage through the piston inner member both of which are connected to the upper fluid chamber. A one-way check valve in the supply passage permits only fluid flow from the supply passage and into the upper chamber while, conversely, a normally closed valve in the discharge passage opens at a predetermined pressure in the upper fluid chamber and permits fluid to discharge through the discharge passage and into the engine crankcase.
In these previously known VCR piston assemblies, it has been the conventional practice to mount and entrap both the supply inlet valve and the normally closed discharge valve between a plate and the top end of the inner piston member. The plate in turn is secured to the inner piston member by bolts or similar fastening means.
These previously known VCR piston assemblies are thus disadvantageous in that virtually total disassembly of the VCR piston assembly is required in order to obtain access to either the inlet or discharge valve assemblies. Such access is required, for example, for inspection, maintenance and/or repair of these valve assemblies.
A further disadvantage of these previously known VCR piston assemblies is that the discharge valve, typically a Bellville washer, is tensioned or prestressed against the mounting plate secured to the upper end of the inner piston member. Since the mounting plate is directly secured to the upper end of the piston inner member, individual adjustment of the tension on the discharge valve was impossible. Rather, variation of the tension of the discharge valve has heretofore required shimming of the discharge valve height.